The insights leading to the present invention were acquired from the needs relating to directionally locating acoustic signal sources. Accordingly the present description of the invention mostly concerns directionally locating acoustic sources. Nonetheless the expert easily understands that this invention is immediately applicable also to locating electromagnetic signal sources. The problem of ascertaining which kind the sources are being located only affects the kinds of sensors used in this invention. In the special case of locating acoustic signals, the sensor configuration is a set of microphones whereas when locating electromagnetic sources the system consists of a set of antennas followed by antenna amplifiers.
Presently procedures are known, which are mathematically complex or demand substantial equipment in order to locate such sources, especially in a field of several sources. If now less equipment is used by reducing the number of sensors, the mathematical complexity relating to source-location discrimination will increase. When locating acoustic signal sources, illustratively the determination of phase differences between acoustic signals simultaneously incident on the microphones of the microphone configuration will be selected.
The objective of the present invention is to propose a directional location method and a corresponding system whereby the cited costs can be drastically reduced.
When using a sensor configuration of at least two electric outputs, and different transfer functionsxe2x80x94in the form of receiving lobes regarding the dependence of the electric output signals on the direction of incidence of the input signalsxe2x80x94are effective between the electromagnetic or acoustic input and the aforementioned at least two electric outputs, then it was observed that by taking the ratio of signals representing the said output signals, a ratio function is formed which is unambiguous relative to the angular position of a source and which is independent of the signal level. In this manner the proposed method unambiguously determines an angular position at minimum design complexity and this method is basic in ascertaining two angular positions per source and to spatially unambiguously determine the source position in the sense of a located beam and/or, in the case of simultaneously active sources, to locate said sources at least within the scope of said cited one angular position. As shall be elucidated farther below, when locating the source position, a position cone results from the cited ratio, the aperture angle of said cone being used as position coordinate.
The unambiguous directional position of a source, that is, the location of a local source beam, is possible in a preferred implementation of the invention by analyzing at least three of the cited ratios, and for that purpose at least three electric outputs are provided each of which is associated with a different transfer function of the above stated kind, that is having different receiving characteristics.
When the method discussed so far is used in an environment holding a single, active signal source, then said source""s position shall be determined. If on the other hand several sources are simultaneously active, a spectrum of angular positions results and a single measurement does not immediately reveal how many sources are active at a particular directional location.
For that purpose a further preferred implementation of the invention proposes carrying out the said generation of ratios several times in time-staggered manner and creating a histogram function from the ratios and correlating said histogram function with the previously determined ratios/incidences dependences and to ascertain therefrom the directional position of at least one source.
This procedure is used preferably both when implementing the method of the invention using two of the cited outputs as well as the implementation using three outputs.
In the proposed histogram function, electromagnetic or acoustic signals from sources that have been active for some extended time will result in equal ratios and this phenomenon leads to accumulating these values in the attained histogram function. When correlated with the dependence of ratio and incidence that was determined beforehand, said accumulating values lead directly to ascertaining the particular at least one angular position of the signal sources active in the field.
In another preferred implementing mode, the output signals from the above mentioned sensor configurations are analyzed in the frequency domain. Considering that the cited transfer characteristics change only within the rolloff range, then it follows that the effect of the frequency will be eliminated when forming the ratio, especially so when the selected transfer characteristics all have the same rolloff behavior. Therefore signal analysis in the frequency domain not only makes it possible to set up the said histogram from time-staggered measurements, but also from the spectrum ratios simultaneously ascertained in the frequency domain.
Preferably the transfer characteristics associated with the particular outputs are selected so that they differ merely by a solid-angle phase shift, i.e. that they xe2x80x9clookxe2x80x9d in a different direction but otherwise are identical.
The method of the invention and the system of the invention are especially well suited in locating acoustic sources and, because of the simple equipment and low need for computation, they are especially applicable to hearing aids.